The process as disclosed is particularly applicable to recovery of usable products from waste streams from soybean oil refining and soybean oil hydrogenation but with minor changes should be applicable to other types of waste streams from edible oil refining.
Crude soybean oil is refined to remove free fatty acids, phosphatides, gum, settlings, coloring matters such as chlorophyll, xanthophyll, and miscellaneous unsaponifiable materials.
The first step in the crude oil refining is the degumming process, wherein phospholipids are removed. in the following steps the degummed oil is treated with sodium hydroxide to remove free fatty acids and residual or remaining trace amounts of phospholipids. Neutral oils are then recovered by centrifugation. The next step in the process is a bleaching process which uses acid activated clay and/or carbon to absorb and remove products such as chlorophyll, xanthophyll, peroxides and their breakdown products to improve flavor and produce oil with acceptable flavor and stability. During the bleaching process about 0.3 to 1.5 percent by weight of the bleaching clay is heated to 212 to 248 degrees Fahrenheit for about fifteen minutes. The bleaching clay is separated from the oil by filtration and each pound of the clay absorbs about 0.4 pounds of the oil. The used clay containing the absorbed oil is usually discarded as waste material. The oil lost in this fashion is estimated to be about 110,687 tons per year. One of the objectives of the invention is recovery of the edible oil from this waste stream when either carbon or bleaching clay is used. Note that the final step in the purification is deodorization.
The hydrogenation process is quite generally a batch process using a nickel catalyst. Depending upon the time of hydrogenation,temperature, catalyst concentration pressure etc.. the hydrogenated product may be very fluid, semi-sold, or quite firm.
When the hydrogenation batch is complete the hydrogenated product is circulated through a filter coated with filter aid until the oil is free of nickel. The filter aid and nickel catalyst may be reused several times. When the catalyst is exhausted the exhausted mixture can be processed to recover the nickel.
The invention provides for a novel versatile process to recover edible oil from both process waste streams. An extractor and a desolventizer pair is used for each process waste stream and since the same solvent may be used to dissolve either the unhydrogenated or hydrogenated oil a common solvent recovery system is used. In a first operating mode the waste stream containing filter aid and nickel catalyst is fed through an extractor wherein the hydrogenated oil is dissolved out of the filter aid-nickel catalyst mixture and the oil rich solvent stream is sent to the solvent recovery system. The filter aid-nickel catalyst mixture that may contain as much as 70 percent by weight of the oil is fed to a desolventizer unit that vaporizes the solvent which then feeds to the solvent recovery unit. The solvent free filter aid-nickel catalyst flows to a pelletizer in order that the otherwise free flowing light powder may be fed directly into an electromelt furnace for nickel recovery in the normal manner. The hydrogenated oil from the solvent recovery unit drains completely from the oil stripper in the last stage of the solvent recovery system.
With cessation of feed of the filter aid- catalyst waste stream the feed of the oil-bleaching clay mixture may be started through it's dedicated extractor and desolventizer with the common solvent recovery system continuing to operate. The unhydrogenated oil will then be recovered from the oil stripper in the solvent recovery system and reusable bleaching clay will be recovered from the desolventizer.
In pilot plant use we found that hexane was particularly suited for use as a solvent. The filter aid and catalyst are quite fine and settle very slowly so that a low viscosity solvent is desirable. A low boiling solvent is desirable to facilitate total removal of the solvent from the recovered edible oil in the solvent recovery system. However other inert hydrocarbons, alcohols, halogenated inert hydrocarbons, and mixtures thereof should be usable.